A glass plate has been used in view of thermal stability or transparency, as a base plate of a display such as a liquid crystal display or an organic electroluminescence display or as a base plate of an electronic device such as CCD or a CMOS sensor.
In recent years, as portable information terminal units such as a cellular phone spread, use of a plastic substrate, which is flexible, light and difficult to be damaged, has been studied in place for a glass substrate, which is heavy or easy to be damaged, in a display or an electro-optical device provided in the terminal units.
However, since the plastic substrate has a moisture penetrability, it is difficult to be applied to a device such as an organic electroluminescence display (hereinafter referred to also as an organic electroluminescence element) which is damaged by moisture to cause deterioration of its performance. Accordingly, how to seal moisture is a problem.
In order to overcome the above problem, in WO-0036665 is proposed a layer (hereinafter referred to as proposed prior art) with a high moisture sealing ability, a composite layer employing silica with a low moisture penetrability and an acryl monomer, which is formed by depositing on a substrate a monomer containing an acryl monomer, polymerizing the deposited monomer, depositing silica, and further depositing a monomer containing an acryl monomer and polymerizing the deposited monomer. However, in this literature, concrete materials used or concrete experiment conditions are not disclosed. The present inventors have traced the proposed prior art, and as a result, they have found that the proposed prior art has problem in that the formed polymer layer and inorganic substance layer are likely to exfoliate during handling and moisture penetrates in the portions where the layers exfoliate.